Reverse DNS is a function of your provider's DNS and not the one on your server!

The good news is I have never run into a provider that charges to setup rDNS
and it's just simply a matter of asking them to set that up and telling them
what hostname you want associated with what IP address.

For any other DNS setup other than reverse DNS, you can do yourself but
reverse DNS needs to be done from your provider.

The only exception to this is if you are running your own network and have
your own IP pool directly allocated from ICANN. If you don't know what
I am talking about then it definitely doesn't apply to you.

Bottom line: Contact your server provider and they will set this up for you.

Some datacenters, I know justedge.net did for me, will delegate your IP block to your server for reverse DNS. I was able to manage it in WHM by adding a DNS zone for in-addr.arpa and making the appropriate entries. For example, 127.0.0.1 would be entered into this zone as 1.0.0.127 IN PTR reverse.record. <- remember the period at the end.